Optimization On Injector Control Circuit Of High Pressure Common Rail`s Electronic Control Unit

Injector drive circuit is an important part of electronic control system. Define when the injector is cut off, the section of circuit which decides the rate of current dropping as freewheeling circuit. Different stages of injector work process need different rate of current dropping. In zero-pulse-width phase and holding phase, lower rate of current dropping can make the injector working stable, make controlling the current value easily and cut the usage of electric energy; in injector closing phase, higher rate of current dropping can reduce the time of injector closing and enhance the control accuracy of the injector. Therefore, the freewheeling circuit determines the performance of the drive circuit.Commonly used injector drive circuit, only uses one mode of freewheeling circuit. So, in injector working process, the rate of current can't be changed. It can't satisfy different rate of current dropping need of different stages of injector working process. In this paper, the concept of freewheeling circuit-switched is brought into injector circuit. In different stages of injector working process, different modes of freewheeling circuit are used to control the rate of current dropping.According to different rate of current dropping need of different stages, D-freewheeling circuit which makes the lowest current dropping rate is chosen to be used in zero-pulse-width phase and holding phase, Non-freewheeling circuit which makes the highest current dropping rate is chosen to be used in injector closing phase. But in closing phase, the dropping rate is so high that the injector solenoid coil will have a great self-induction electromotive force. The damage is that the source of high-side MOS tube takes on a great negative overshoot, and the high-side driver chip is burned. By adding a reverse diode connected to ground, the chip will not burn any more. The mode of freewheeling circuit in closing phase has been changed, but it makes the drive circuit safe. Also the VS pin in high-side drive chip is suspended which result in that the high-side MOS tube can't be open, a pull-down resistor is added to eliminate the suspension. In injector closing phase, due to the diode not full opened, there is also a spike-like negative overshoot which makes the high-side drive chip self-locking. In this case, capacitor is used to slow down the rate of voltage to make sure the diode is full opened before the pike-like negative overshoot occurs. The pull-down resistor can't make the VS pin's voltage to be 0V quickly, so the drive circuit can`t use multiple-pulse. So, the chip IR20153S is chosen to be the high-side drive chip. The chip IR20153S has an ability that the VS pin can pull down itself, high resistance to negative overshoot, an ability to control the high-side MOS tube's power or cutting off independently. When the injector is closed, the VS pin return to 0V faster, so the drive circuit can be applied to the multi-pulse. Finally, a kind layout program of multi-cylinder engine is present to reduce the chips and simplify the circuit.Through brief analyses and experimental verification, the optimized drive circuit has a better energy saving capability and the injecting fuel quantity controlling precision, and achieved good results.